1. Technical Field
The present disclosure relates to an array antenna that radiates a radio wave.
2. Description of the Related Art
An example of an array antenna used for wireless communication system or radar application is an array antenna having a microstrip structure.
For example, Japanese Patent No. 3306592 discloses a microstrip array antenna that includes a plurality of rectangular antenna elements disposed along a linear feed line. Each of the plurality of rectangular antenna elements is connected to the feed line in a direction inclined with respect to the feed line.
In general, it is necessary to suppress unnecessary radiation (side lobe) of a radiated wave in an array antenna. In order to suppress side lobe, a distribution of amplitudes of a plurality of antenna elements constituting the array antenna by weighting the amplitudes of the antenna elements. For example, the amount of radiation of an antenna element in the vicinity of the center is made large, and the amount of radiation of an antenna element is made smaller as the distance from the center becomes larger. For example, the amount of radiation of an antenna element close to an end need to be adjusted to a low amount of radiation of approximately 1% to 2% of the whole amount of radiation from all of the antenna elements in order to make the side lobe lower by 20 dB than a radio wave in a desired radiation direction. In the following description, the amount of radiation relative to the whole amount of radiation from all of the antenna elements is expressed by percentage.
However, in the conventional art of Japanese Patent No. 3306592, the width of each of the plurality of rectangular antenna elements need be set to not more than 50 μm in order to reduce the amount of radiation of the antenna element to approximately 1% to 2%. However, it is difficult to produce an antenna element whose width is not more than 50 μm with pattern etching accuracy in general substrate processing.